Femur Length is Correlated with Isometric Quadriceps Strength in Post-Operative Patients.
Robert S Dean, Nicholas N DePhillipo, Michael T Kiely and 3 others
PMID 35693850WHAT IT FOUND
Longer femurs correlated with stronger quadriceps in healthy knees.
Among ligament reconstruction patients, longer limbs and femurs correlated with smaller strength deficits. Tibia length showed no such relationship. These links were weak to moderate, and the study was small and single-surgeon.
Key findings
01Femur length in the non-surgical limb was significantly correlated with peak quadriceps torque (r=0.43, p=0.048), while tibia and total limb length were not.
02In ligament reconstruction patients excluding those with contralateral patellar tendon harvest, longer limb length and femur length correlated with smaller quadriceps strength deficits (r=-0.47 and r=-0.51 respectively).
03The surgical limb demonstrated significantly lower peak torque, average peak torque, and average peak torque to bodyweight compared to the non-surgical limb (p<0.001).
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The sample was small (40 patients) and drawn from a single surgeon's practice, which limits generalizability. Post-hoc power analysis showed 81 percent power, but no a priori power calculation was performed. Full-length weightbearing radiographs are not routinely available in physical therapy clinics, and manual reproduction of the measurement technique is difficult. Patients were tested at varying post-operative intervals (range 3.5 to 15.1 months), which introduces variability in recovery status. Muscle volume and cross-sectional area were not measured, so the relationship between bone length and actual muscle mass remains unclear. Confounding variables such as pain, swelling, and arthrogenic muscle inhibition were not controlled for. The significant correlations were weak to moderate (r=0.43 to 0.51), and the study was explicitly framed as a pilot for future reference.
Declared interests
The authors report no conflicts of interest.
The easy way to misread this
Do not adopt femur length as a clinical normalization factor for quadriceps strength testing. The correlations were weak to moderate, the sample was small and single-surgeon, and the authors themselves state this study should serve only as a pilot for future reference.